Image sensing and processing apparatus and method

ABSTRACT

Image sensing and processing apparatus in which the different colors of a subject are sensed to provide a high resolution electrical color separation signal and a low resolution electrical color separation signal. An enhanced high resolution electrical color separation signal is thereafter provided as a function of the color matrixing of the low resolution electrical color separation signals with the high resolution electrical color separation signals.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to an image sensing and processingapparatus and, more particularly, to an electronic image sensing andprocessing apparatus for providing an enhanced electrical output signal.

2. Description of the Prior Art

Electronic image scanning and processing apparatus embodying a chargetransfer type of scanning device such as a CCD fabricated in the form ofan integrated circuit on a thin silicon semiconductor substrate are wellknown in the art.

It is also well known to utilize such apparatus to scan a subject suchas a color negative or transparency or a positive or a document andprocess the information derived therefrom to provide a facsimile of thesubject in enhanced or corrected colors. Such apparatus sense thesubject and introduce a color correction factor so that each color has apredetermined density and displays the subject with a corrected color asdisclosed in U.S. Pat. No. 3,644,664, entitled "Correction LevelAdjustment for Video Negative Analyzer", by Robert Huboi et al., issuedFeb. 22, 1972. Huboi et al. recognized that prior art color analyzingand correction devices were deficient in not taking into account theeffect that one color may have on another color in determining thedegree of color correction that should be imparted to the image. Towardthat end well-known color correction equations are utilized in whicheach red, green and blue primary color is corrected as a function of allthree primary colors. As is readily apparent, in order to provide suchcolor correction it is necessary that the red, green and blue colorsignals be available at all times despite the fact that the subject isgenerally scanned through red, green and blue light filter elements witheach filter element moved in sequence over the light sensing device.Huboi et al. manages to provide continuous red, green and blue colorseparation signals through complex circuitry that continuouslydetermines each color separation signal as a function of the other colorscanned during those intervals in which that color is not directlyscanned. Continuous red, green and blue color separation signals canalso be provided during the sequential red, green and blue color filterscan of the subject by storing in image memory those color signalcomponents scanned through the immediately preceding color filter in thesequence. Such image memories, however, must have large storagecapacities in order to accommodate the large volume of image data thatmust be stored for each of the two primary colors not being immediatelyscanned. This memory storage capacity requirement must be even furtherincreased when the electronic image data is converted from an analogformat to a digital format in order to provide a high quality facsimileof the subject.

Therefore, it is a primary object of this invention to provide anelectronic image sensing and processing apparatus in which the red,green and blue color separation signals are each enhanced as a functionof the other color separation signals utilizing a minimum storagecapacity memory.

It is a further object of this invention to provide an electronic imagesensing and processing apparatus in which the primary red, green andblue color separation signals are sensed in high resolution and thecyan, magenta and yellow color separation signals are sensed in lowresolution to provide full color correction or enhancement utilizing aminimum capacity image memory to store the low resolution cyan, magentaand yellow color separation signals.

Other objects of the invention will be in part obvious and will in partappear hereinafter. The invention accordingly comprises a mechanism andsystem possessing a construction, combination of elements andarrangement of parts which are exemplified in the following detaileddisclosure.

DESCRIPTION OF THE DRAWINGS

The novel features that are considered characteristic of the inventionare set forth with particularity in the appended claims. The inventionitself, however, both as to its organization and its method ofoperation, together with other objects and advantages thereof will bebest understood from the following description of the illustratedembodiment when read in connection with the accompanying drawingswherein:

FIG. 1 is a schematic block diagram for the image sensing and processingapparatus of this invention;

FIG. 2 is a front view of the filter wheel arrangement utilized in theimage sensing and processing apparatus of FIG. 1; and

FIG. 3 is a graphical representation for various clock pulse trainsprovided by various clocks in the image sensing and processing apparatusof FIG. 1.

SUMMARY OF THE INVENTION

Image sensing and processing apparatus comprise a photoresponsive meansfor sensing different colors of image defining light incident theretofor each picture element of a selected number of image defining pictureelements and providing a high resolution electrical color separationsignal corresponding to each color selected and sensed for each one ofthe picture elements. The photoresponsive means also provides a lowresolution electrical color separation signal corresponding to eachcolor selected and sensed for groupings of the image defining pictureelements. Means are included for storing in memory the low resolutionelectrical color separation signals. Signal processing means respond tothe low resolution electrical color separation signals retrieved fromthe memory and the high resolution electrical color separation signalssensed by the photoresponsive sensing means for providing enhanced highresolution electrical color separation signals. There may also beincluded means responsive to the enhanced high resolution electricalcolor separation signals for providing an enhanced facsimile of theimage so detected by the photoresponsive means.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1, there is shown a schematic block diagram for anelectronic image sensing and processing system which embodies the colormatrix image enhancement feature of this invention. A document,photograph or slide transparency to be electronically sensed andprocessed is shown generally at 12 in position to be line scanned by aCCD linear image sensor as shown generally at 20. A filter wheel asshown generally at 14 comprising a plurality of circumferentially spacedapart individual light filtering elements is disposed between thesubject 12 to be scanned and the linear image sensor 20 so as to filterthe image defining light rays sensed by the linear image sensor 20.

The linear image sensor 20 comprises a line of light sensor orphotoresponsive elements or pixels (1 through N) as shown generally at24. The line of sensor elements 24 is comprised of single crystalsilicon in which the image photons create electron hole pairs. Theelectrons are collected in the individual sensor elements (1 through N),and the holes are swept into the substrate. The amount of chargeaccumulated in each sensor element (1 through N) is a linear function ofthe incident light and the exposure time, and the output signal chargewill vary in an analog manner from a thermally generated noisebackground at zero illumination to a maximum at saturation under brightillumination.

Adjacent one side of the line of image sensor elements 24 there isprovided an odd pixel transfer gate 26, and adjacent the other side ofthe line of image sensor elements 24 there is provided an even pixeltransfer gate 28. Adjacent the odd and even pixel transfer gates 26 and28, there is provided respectively an odd pixel CCD transport shiftregister 30 and an even pixel CCD transport shift register 32. Thetransfer of charge from the individual sensor elements 24 to thetransport shift registers 30, 32 by way of the transfer gates 26, 28respectively is controlled by a transfer clock as shown at 50. Thecharge packets accumulated in the individual sensor elements 24 aretransferred into storage wells of respective ones of the odd/even pixeltransfer gates 26, 28 when the transfer gate clock voltage from theclock 50 goes high. When the transfer gate clock voltage from the clock50 goes low, the charge packets are transferred from respective storagewells of the odd/even pixel transfer gates 26, 28 into correspondingones of the odd/even transport shift registers 30 and 32. Thus, in thismanner the odd/even pixel transfer gates 26 and 28 operate to controlthe exposure time for the sensor elements 24.

Alternate charge packets transferred to the odd/even CCD transport shiftregisters 30 and 32 are thereafter moved serially to a charge detectiondiode as shown generally at 34 by a transport clock pulse train providedfrom a transport clock 52. The charge packets are alternatelytransported by the transport clock pulse train from the transport clock52 to the charge detection diode whose potential changes linearly inresponse to the amount of the signal charge delivered thereto. Thepotential at the charge detection diode 34 is applied to the input gateof a cascaded source follower MOS amplifier 36 which, in turn, operatesto provide an electrical output signal. The charge detection diode 34 isreset before the arrival of each new signal charge packet from the CCDtransport shift registers 30 and 32 by a reset clock pulse trainprovided by a reset clock 54. The phase relationship of the reset clockpulse train provided by the reset clock 54 and the transport clock pulsetrain provided by the transport clock 52 and the geometric layout of thepaths provide for alternate delivery of charge packets to reestablishthe original sequence of the linear image data.

The electrical output signal from the cascaded source follower MOSamplifier 36, in turn, is directed to an analog-to-digital converter 38from which the analog signal is converted to a digital signal for eachsensor element. The digitized image data, in turn, is directed to anarithmetic logic unit as shown generally at 40 for multiplication by aconstant factor (-K). In its preferred form the arithmetic logic unit 40may comprise a lookup table. After multiplication by the constant factor(-K), the digitized data from the arithmetic logic unit 40 is thereafterdirected for storage in an image memory as shown generally at 42 whichin its preferred mode may comprise a random access memory (RAM).

Digitized image data from the analog-to-digital converter 38 is alsodirected to another arithmetic logic unit 44 for multiplication byanother constant factor (1+2K). Again, the arithmetic logic unit 44 inits preferred form comprises a lookup table. The digital output signalfrom the arithmetic logic unit 44, in turn, is directed to an addercircuit 46 for combination with the output from the RAM 42. The outputsignal from the adder 46, in turn, represents an enhanced electricaloutput signal which may thereafter be directed to a printer 48 fromwhence an enhanced image facsimile of the subject 12 originally scannedmay be provided in the usual manner. The printer 48 may be anyconventional well-known electronic facsimile recording device such as athermal printer, a CRT printer, or a laser printer.

Referring now to FIG. 2, there is shown the preferred arrangement ofthis invention for the circumferentially spaced apart filter elements ofthe filter wheel 14. As is readily apparent from the drawing, the filterwheel 14 comprises the primary colored red, green and blue filterelements alternately disposed with respect to the complementary coloredyellow, cyan and magenta filter elements.

Image enhancing color correction is provided in the manner of thisinvention using standard color matrixing in accordance with thefollowing equations where K may typically be in the order of 0.3.

    B"=(1+2K)B-KR-KG

    R"=(1+2K)R-KB-KG

    G"=(1+2K)G-KR-KB

B", R" and G" represent the enhanced electrical color separationsignals. These color matrixing equations can be rewritten in terms ofthe complementary colors yellow, cyan and magenta as follows.

    B"=(1+2K)B-K Yellow

    R"=(1+2K)R-K Cyan

    G"=(1+2K)G-K Magenta

Operation of the image sensing and processing system 10 may commence byrotatably driving the filter wheel 14 with a motor 16 into position suchthat the subject 12 can be line scanned by the linear image sensor 20through the yellow filter. The line of sensor elements 24 may compriseapproximately 1,000 individual sensing elements or pixels and may bemoved transversely across the face of the item 12 by the motor 22 in thedirection as shown by the arrow A. As previously discussed, electronsare collected in the individual sensor elements and the holes are sweptinto the substrate such that the amount of charge accumulated in eachsensor element is a linear function of the incident light and theexposure time. The complementary colors yellow, cyan and magenta aresensed in low resolution equivalent to a 250×250 pixel matrix scan inthe manner of this invention to be subsequently described as contrastedwith the primary colors red, green and blue which are sensed at fullresolution equivalent to a 1,000×1,000 pixel matrix scan.

As previously discussed, the transfer clock 50 as shown in FIG. 3controls the transfer of charge packets from the sensor elements 24 tothe transport shift registers 30, 32 and thus the interval between thepulses of the transfer clock pulse train determines the exposure timefor each sensing element. The transfer clock pulse train for a fullresolution 1,000×1,000 pixel matrix scan is shown at A in FIG. 3 alongwith the accompanying transport and reset clock pulse trains as shown atB and C which control respectively the transport of charge packets fromthe shift registers 30 and 32 and the recharging of the charge detectiondiode 34 for each charge packet received from the transport shiftregisters 30 and 32. The full resolution 1,000 by 1,000 pixel matrixscan may be reduced to a low resolution 250×250 pixel matrix scan in themanner of this invention by changing the transfer clock pulse train andtransport clock pulse train as shown at D and E in FIG. 3 whilesimultaneously increasing the speed of the motor 22 to drive the linearimage sensor 20 across the item 12 in the direction of the arrow A atquadruple the speed at which the full resolution 1,000×1,000 pixelmatrix scan is made.

As is readily apparent from FIG. 3, the frequency of the transfer clockpulse train D is also quadrupled so as to provide one-fourth theexposure time as that provided by the transfer clock pulse train A. Withone-fourth the exposure time for each light sensing element there canthus only be accumulated one-fourth the charge packets for each lightsensing element as would otherwise be accumulated for the transfer clockpulse train A. Thus, each light sensing element accumulates one-fourththe charge packets as would otherwise be accumulated during the fullresolution scan. The transport clock pulse train frequency in E for thelow resolution 250×250 pixel matrix scan, in turn, is also quadrupled incomparison to the frequency of the transport clock pulse train B for thefull resolution 1,000×1,000 pixel matrix scan. Thus, the chargedetection diode 34 receives charge packets at four times the rate forthe low resolution scan as for the high resolution scan so as to allowthe charge packets from four sensing elements to accumulate prior toeach reset. Since as previously discussed each sensing elementaccumulates only one-fourth the charge packets it would otherwiseaccumulate during the full resolution scan, resetting the chargedetection diode 34 after receiving the charge packets from four sensingelements operates to provide an analog output value equivalent to theaverage value of four linear picture sensing elements. Thus, in thismanner can low resolution average values be provided for a predeterminednumber of linear sensing elements. Vertical averaging is provided simplyby increasing the vertical scan rate by scanning over four horizontallines in the same time as a single horizontal line scan would otherwisebe made. Thus, in this manner can a low resolution 250×250 pixel matrixscan be made.

The subject 12 is thus fully line scanned through the yellow filter toprovide a low resolution analog electrical output signal from thecascaded source follower MOS amplifier 36 to the analog-to-digitalconverter 38. The analog electrical output signal, in turn, is convertedto a digitized signal and thereafter directed to the arithmetic logicunit 40 in which the digitized data is multiplied by the factor (-K).The modified output signal from the arithmetic logic unit 40 isthereafter directed to the (RAM) 42 for temporary storage.

The filter wheel 14 is thereafter incrementally rotated so as to bringthe blue filter into position between the subject 12 and linear imagesensor 20 for the next line scan operation. As previously discussed, theline scan through the blue filter element is conducted at fullresolution to provide the 1,000×1,000 pixel matrix scan utilizing thetransfer clock pulse train A and the transport clock pulse train B ofFIG. 3. As previously discussed, the motor 22 is operated at one-fourththe speed previously utilized during the line scan through the yellowfilter element to provide the full resolution output. The electricaloutput signal from the cascaded source follower MOS amplifier 36, inturn, is directed to the analog-to-digital converter 38 for conversionto a digital signal which, in turn, is directed to the arithmetic logicunit 44 for multiplication by the factor (1+2K). The output signal foreach pixel from the arithmetic logic unit 44, in turn, is added to theoutput signal for the corresponding low resolution pixel retrieved fromthe (RAM) 42 representative of the previous line scan through the yellowfilter. Thus, the adder 46 provides an enhanced output blue color signalin accordance with the first modified color matrix equation. Theenhanced blue color signal may be thereafter directed to the printer 48to print the blue primary color in the usual manner.

The filter wheel 14 is next incrementally rotated by the motor 16 tomove the cyan filter into position between the subject 12 and imagesensor 20 in order to enable the next line scan to be made through thecyan filter element. As previously discussed, the line scan through thecyan filter element is made at the low resolution 250×250 pixel matrixscan utilizing the transfer clock pulse train D and transport clockpulse train E of FIG. 3. The low resolution video signal is convertedfrom an analog-to-digital value in the aforementioned manner by theanalog-to-digital converter 38 and thereafter directed to the arithmeticlogic unit 40 for multiplication by the factor (-K). The low resolutioncyan video signal is thereafter stored in the (RAM) 42.

The filter wheel is thereafter incrementally rotated by the motor 16 soas to move the red filter element into position between the subject 12and the image sensor 20 so as to enable the next line scan to be madethrough the red filter element. As previously discussed, the line scanof the subject 12 through the red filter element is made at the fullresolution 1,000×1,000 pixel matrix scan using the transfer clock pulsetrain A and transport clock pulse train B of FIG. 3. The high resolutionoutput video signal from the cascaded source follower MOS amplifier 36is converted by the analog-to-digital converter 38 to a digital valueand thereafter multiplied by the factor (1+2K) by the arithmetic logicunit 44. The multiplied output signal for each pixel from the arithmeticlogic unit 44, in turn, is added to the cyan signal for eachcorresponding low resolution pixel previously stored in the (RAM) 42.The output from the adder 46 thus provides an enhanced red color signalin accordance with the second modified color matrix equation. Theenhanced red color signal is thereafter utilized in the usual manner bythe printer 48 to print the red color component of the hard copy.

The filter wheel 14 is thereafter incrementally rotated by the motor 16to drive the magenta filter element into position between the subject 12and the image sensor 20. The image sensor 20 thereafter completesanother line scan of the subject 12 at the aforementioned low resolution250×250 pixel matrix scan utilizing the transfer clock pulse train D andthe transport clock pulse train E of FIG. 3. The low resolution videooutput signal from the cascaded source follower MOS amplifier 36 isthereafter converted to a digital signal by the analog-to-digitalconverter 38. The digitized. signal, in turn, is directed formultiplication by the factor (-K) by the arithmetic logic unit 40 fromwhence it is transferred for storage in the (RAM) 42.

The filter wheel is thereafter incrementally driven by the motor 16 tomove the green filter element into position between the subject 12 to beline scanned and the linear image sensor 20. The image sensor 20 thusline scans the item 12 through the green filter element to provide ahigh resolution 1,000×1,000 pixel matrix scan utilizing the transferclock pulse train A and the transport clock pulse train B of FIG. 3. Thehigh resolution video signal, in turn, is converted by the AD converter38 to a digital signal and thereafter multiplied by the factor (1+2K) bythe arithmetic logic unit 44. The digital output signal for each pixelmodified by the factor (1+2K) is thereafter added to the previouslysensed magenta digital signal for each corresponding low resolutionpixel from the (RAM) 42 to provide an enhanced green output signal inthe manner of the third line of the modified color matrix equations. Theenhanced green color signal is thereafter directed to the printer 48 forprinting in the usual manner of the green colored component of the hardcopy.

In this manner, color matrixing can be accomplished in a simple andeconomical manner utilizing a minimum capacity memory, i.e., (RAM) 42,having sufficient memory to hold digital image data for only a 250×250pixel array. In addition to the aforementioned color correction orenhancement, the system of this invention also provides for an apparentenhancement in image sharpness. The memory capacity storage requirementsfor the random access memory (RAM) 42 are thus reduced by sensing thecomplementary yellow, cyan and magenta color components in lowresolution in comparison to the high resolution in which the primaryred, green and blue color components are sensed. It should be readilyunderstood that although the preferred embodiment utilizes anarrangement of filter elements to sense the subject in both the primaryred, green and blue color components as well as the complementaryyellow, cyan and magenta color components, the invention is by no meansso limited and color matrixing could be accomplished in accordance withthe first set of color matrixing equations in which case only theprimary color actually being enhanced would be sensed in high resolutionwhile the remaining two primary colors to be color matrixed therewithwould be sensed in low resolution.

Other embodiments of the invention, including additions, subtractions,deletions and other modifications of the preferred disclosed embodimentsof the invention will be obvious to those skilled in the art and arewithin the scope of the following claims.

What is claimed is:
 1. Image sensing and processing apparatuscomprising:photoresponsive means for sensing different colors of imagedefining light incident thereto for each picture element of a selectednumber of image defining picture elements, and providing a highresolution electrical color separation signal corresponding to eachcolor selected and sensed for each one of said picture elements and alow resolution electrical color separation signal corresponding to eachcolor selected and sensed for selected groupings of said image definingpicture elements; means for storing in memory the low resolutionelectrical color separation signals; and signal processing meansresponsive to the low resolution electrical color separation signalsretrieved from said memory and the high resolution electrical colorseparation signals sensed by said photoresponsive sensing means forproviding enhanced high resolution electrical color separation signalsfor said selected color.
 2. The apparatus of claim 1 wherein said signalprocessing means operates to color matrix each color component of saidhigh resolution electrical color separation signal with a select colorcomponent of said low resolution electrical color separation signal toprovide said enhanced high resolution electrical color separationsignals.
 3. The apparatus of claim 2 wherein the colors selected forsaid high resolution electrical color separation signal are selectedfrom the group of primary red, green and blue colors and the colorsselected for said low resolution electrical color separation signals areselected from the group of complementary cyan, magenta and yellowcolors.
 4. The apparatus of claim 2 wherein said photoresponsive meanscomprises a linear array of light sensing elements for providing a linescan of a subject wherein each one of said light sensing elementscorresponds to one of said image defining picture elements and means forestablishing relative movement between said linear array and the subjectto be scanned in a direction transverse to the direction of said linescan in order to enable said linear array to scan the entire area of thesubject.
 5. The apparatus of claim 2 further including means responsiveto the enhanced high resolution electrical color separation signals forproviding an enhanced facsimile of the image so detected by saidphotoresponsive means.
 6. Image sensing and processing apparatuscomprising:photoresponsive means for sensing different colors of imagedefining light incident thereto for each picture element of a selectednumber of image defining picture elements, and providing a highresolution electrical color separation signal corresponding to eachcolor selected and sensed for each one of said picture elements and alow resolution electrical color separation signal corresponding to eachcolor selected and sensed for selected groupings of said image definingpicture elements; means for storing in memory the low resolutionelectrical color separation signals; and signal processing meansresponsive to the low resolution electrical color separation signalsretrieved from said memory and the high resolution electrical colorseparation signals sensed by said photoresponsive sensing means forproviding enhanced high resolution electrical color separation signalsfor said selected color wherein: said signal processing means operatesto color matrix each color component of said high resolution electricalcolor separation signal with a select color component of said lowresolution electrical color separation signal to provide said enhancedhigh resolution electrical color separation signals, saidphotoresponsive means comprises a linear array of light sensing elementsfor providing a line scan of a subject wherein each one of said lightsensing elements corresponds to one of said image defining pictureelements and means for establishing relative movement between saidlinear array and the subject to be scanned in a direction transverse tothe direction of said line scan in order to enable said linear array toscan the entire area of the subject, and said photoresponsive meansfurther comprises a transfer register for receiving and transferringindividual charge packets from said sensing elements, transfer gate andclock means for controlling the transfer of said charge packets fromsaid linear array to said transfer register, a precharge diode forproviding an analog output potential in correspondence to the chargetransferred thereto from said transfer register and transport clockmeans for controlling the transfer of said charge packets from saidtransfer register to said precharge diode wherein the output from saidphotoresponsive means is varied from said high resolution electricalcolor separation signal to said low resolution electrical colorseparation signal by increasing the speed of said relative movementbetween said linear array and the subject to be scanned, by increasingthe rate at which said transfer gate and clock means controls thetransfer of said charge packets from said linear array to said transferregister, and by increasing the rate at which said transport clock meanscontrols the transfer of said charge packets from said transfer registerto said recharge diode.
 7. A method for electronically sensing an imageand processing the electronic signal information so sensed comprisingthe steps of:sensing different colors of an image defining lightincident thereto for each picture element of a selected number of imagedefining picture elements and providing a high resolution electricalcolor separation signal corresponding to each color so sensed for eachone of said picture elements and a low resolution electrical colorseparation signal corresponding to each color so sensed for selectedgroupings of said image defining picture elements; storing in memory thelow resolution electrical color separation signals; and providingenhanced high resolution electrical color separation signals for aselected color from the low resolution electrical color separationsignals stored in said memory and the high resolution electrical colorseparation signals sensed by said photoresponsive sensing means for saidselected color.
 8. The method of claim 7 further comprising the steps ofcolor matrixing each color component of said high resolution electricalcolor separation signal with a select color component of said lowresolution electrical color separation signal to provide said enhancedhigh resolution electrical color separation signals.
 9. The method ofclaim 8 further comprising the step of selecting the colors for saidhigh resolution electrical color separation signal from the group ofprimary red, green and blue colors and selecting the colors for said lowresolution electrical color separation signal from the group ofcomplementary cyan, magenta and yellow colors.
 10. The method of claim 7wherein said light sensing is accomplished by line scanning with alinear array of light sensing elements each one of which corresponds toone of said image defining picture elements and establishing relativemovement between said linear array and the subject to be scanned in adirection transverse to the direction of said line scanning therebyenabling said linear array to scan the entire area of the subject. 11.The method of claim 10 further including the steps of: receiving andtransferring individual charge packets from said sensing elements to atransfer register and controlling the rate of transfer of said packets,with a transfer gate and clock pulse, transferring the charge packetsfrom said transfer register to a precharge diode to provide an analogoutput potential in correspondence to the charge transferred therein,and periodicaly resetting the potential of said precharge diode.
 12. Themethod of claim 7 further including the step of making an enhancedfacsimile the subject responsive to said high resolution electricalcolor separation signals.
 13. A method for electronically sensing animage and processing the electronic signal information so sensedcomprising the steps of:sensing different colors of an image defininglight incident thereto for each picture element of a selected number ofimage defining picture elements and providing a high resolutionelectrical color separation signal corresponding to each color so sensedfor each one of said picture elements and a low resolution electricalcolor separation signal corresponding to each color so sensed forselected groupings of said image defining picture elements; storing inmemory the low resolution electrical color separation signals; andproviding enhanced high resolution electrical color separation signalsfor a selected color from the low resolution electrical color separationsignals stored in said memory and the high resolution electrical colorseparation signals sensed by said photoresponsive sensing means for saidselected color, said method further comprising the steps of colormatrixing each color component of said high resolution electrical colorseparation signal with a select color component of said low resolutionelectrical color separation signal to provide said enhanced highresolution electrical color separation signals, wherein said lightsensing is accomplished by line scanning with a linear array of lightsensing elements each one of which corresponds to one of said imagedefining picture elements and establishing relative movement beween saidlinear array and the subject to be scanned in a direction transverse tothe direction of said line scanning thereby enabling said linear arrayto scan the entire area of the subject, said method further includingthe steps of: receiving and transferring individual charge packets fromsaid sensing elements to a transfer register and controlling the rate oftransfer of said packets, with a transfer gate and clock pulse,transferring the charge packets from said transfer register to aprecharge diode to provide an analog output potential in correspondenceto the charge transferred therein, and periodically resetting thepotential of said precharge diode in which the said high resolutionelectrical color separation signal is changed to said low resolutionelectrical color separation signal by the steps of: increasing the speedof said relative movement between said linear array and the subject tobe scanned, increasing the rate at which said charge packets aretransferred from the linear array to the transfer register, andincreasing the rate at which said charge packets are transferred fromthe transfer register to the precharge diode.